Chronic paroxysmal hemicrania (CPH), also known as Sjaastad syndrome, was first described in 1974, by Sjaastad and Dale. In 1976, the term CPH was proposed by Sjaastad on the basis of the first 2 patients, who had daily (ie, chronic), solitary, limited attacks (ie, paroxysmal) of unilateral headache that did not shift sides (ie, hemicrania).
CPH falls under the Trigeminal Autonomic Cephalalgias (TACs); it accounts for about 3%–8% of TACs and is much less common than cluster headache (CH). (See Presentation.)
The short-lasting primary headache syndromes may be divided into (1) headaches with autonomic activation and (2) headaches without autonomic activation. Headaches with autonomic activation include chronic and episodic paroxysmal hemicrania, CH, and short-lasting unilateral neuralgiform headache with conjunctival injection and tearing (SUNCT syndrome). (See Etiology and DDx.)
In the current International Classification of Headache Disorders (ICHD-3), TACs include cluster headache (CH), paroxysmal hemicrania (PH), and the short-lasting unilateral neuralgiform headache attacks (SUNHAs).
ICHD-3 diagnostic criteria for PH include the following:
A. At least 20 attacks of headache fulﬁlling criteria B–E
B. Severe unilateral orbital, supraorbital and/or temporal pain lasting 2–30 minutes
C. Either or both of the following:
- at least one of the following symptoms or signs, ipsilateral to the headache: a) conjunctival injection and/or lacrimation, b) nasal congestion and/or rhinorrhoea, c) eyelid oedema, d) forehead and facial sweating, e) miosis and/or ptosis
- a sense of restlessness or agitation
D. Occurring with a frequency of >5 per day
E. Prevented absolutely by therapeutic doses of indomethacin
F. Not better accounted for by another ICHD-3 diagnosis
Chronic versus nonchronic
PH may be present in nonchronic or chronic form, although the chronic type is 4 times more common. Approximately 65%–85% of patients with PH have the chronic form.
Nonchronic attacks are similar to chronic ones but tend to be less severe and less frequent. (See Prognosis.)
Before the development of chronic symptoms, many patients (42%) pass through a nonchronic stage, with attacks separated by intervals of complete remission.
The term pre-CPH stage or prechronic was preferred initially on the basis of the assumption that all patients would develop chronic symptoms. However, approximately 20% of patients appear to remain in the nonchronic stage for long periods.
ICHD-3 diagnostic criteria for CPH are as follows:
A. Attacks fulfilling criteria for Paroxysmal hemicrania, and criterion B below
B. Occurring without a remission period, or with remissions lasting < 3 months, for at least 1 year
The mechanisms responsible for pain in CPH remain unknown. The past medical history in patients with CPH is usually unremarkable. A history of head or neck trauma is reported in about 20% of cases, but these findings are similar to those for CH or migraine.
Occasionally, attacks may be provoked mechanically by bending or rotating the head and by applying external pressure against the transverse processes of C4-C5, C2 root, or the greater occipital nerve.
No familial disposition is known for CPH; families of affected individuals do not have higher incidences of CH or migraine than does the general population.
Discussion of important features, such as intense, unilateral headache; autonomic abnormalities; and effectiveness of indomethacin, may help in understanding the pathogenesis.
Trigeminal, sympathetic, and parasympathetic involvement
The release of trigeminal and parasympathetic neuropeptides during headache has been described. Activation of the ipsilateral trigeminovascular system may explain sudden, unilateral headache and may lead to miosis, increased intraocular pressure (IOP), and other autonomic abnormalities.
Increased sweating and decreased salivation during attacks and the ability of an alpha-blocking agent or a stellate ganglion blockade to inhibit an increase in IOP suggest sympathetic involvement.
Increased tearing, nasal secretion, and miosis may be due to parasympathetic stimulation. Trigeminoparasympathetic activation during CPH attacks has been suggested; increases in the vasoactive intestinal peptide (ie, parasympathetic peptide) level have been reported. levels of calcitonin gene-related peptide also are reported to be high during CPH attacks.
Pain and pressure threshold, nociceptive flexion reflex, and blink and corneal reflexes have been studied in patients with CPH. The corneal reflex thresholds have been found to be decreased bilaterally during CPH attacks. Increases in corneal temperature on the symptomatic side also have been reported; this finding may be due to increased ocular blood flow.
The effectiveness of indomethacin in CPH may be due partly to reduction of intracranial blood flow (via a nonprostaglandin mechanism) and partly to the drug’s anti-inflammatory effects.
These findings may indicate a primary central mechanism and a secondary involvement of peripheral factors, affecting the sympathetic and parasympathetic systems.
Studies have suggested a crucial role by the hypothalamus in CPH. Functional neuroimaging studies have demonstrated activation of the hypothalamus in cases of trigeminal autonomic cephalgias.